Exterior foundation waterproofing involves applying an impermeable membrane barrier to the exterior of a foundation. The best time to use this technique is during new construction when freshly built foundation walls are exposed. Once the foundation walls are covered with dirt, installing an exterior waterproof coating or membrane becomes prohibitively expensive and much more disruptive if the house is occupied.
Interior foundation waterproofing involves applying a special coating (waterproof paint) to the inside walls of a foundation. Although this technique is less disruptive and can be done at any time post construction, it rarely works if the surrounding soils stay wet. With significant hydrostatic (water) pressure against foundation walls, moisture will eventually seep through causing the special coating to bubble, peel and leak.